What is the best way and cheap way to whiten your teeth?

Im just trying to find a cheap way to whiten my teeth,a homemade suggestion possibly?
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I use bicarbonate of soda, not meant to use it a lot cos it's an abrasive but i used it once then again 3 days later then again 3 days later but now i won't do it for a month. After the 3rd time of doing it i noticed a big difference. I used a teaspoon of soda and made it into a paste by adding a little water then brushed with it for about 4 mins. Rinse really well as you don;t want the soda left on your teeth. Then floss to get it all out.
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